1. Field of the Invention
Embodiments of the present invention relate generally to lithium-ion batteries, and more specifically, to a method of fabricating such batteries using thin-film deposition processes.
2. Description of the Related Art
Fast-charging, high-capacity energy storage devices, such as supercapacitors and lithium (Li) ion batteries, are used in a growing number of applications, including portable electronics, medical devices, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supplies (UPS). In modern rechargeable energy storage devices, the current collector is made of an electric conductor. Examples of materials for the positive current collector (the cathode) include aluminum, stainless steel, and nickel. Such collectors can be in the form of a foil, a film, or a thin plate, having a thickness that generally ranges from about 6 to 50 μm.
The active electrode material in the positive electrode of a Li-ion battery is typically selected from lithium transition metal oxides, such as LiFePO4, LiMn2O4, LiCoO2, LiNiO2, or combinations of Li, Ni, Mn, and Co oxides and includes electroconductive particles, such as carbon black or graphite, and a binder material. Such positive electrode material is considered to be a lithium-intercalation compound, in which the quantity of conductive material is in the range from 0.1% to 15% by weight.
The active materials are dispersed in a polymeric binder matrix and then applied to the current collector. The polymers for the binder matrix are made of thermoplastic polymers including polymers with rubber elasticity. The polymeric binder serves to bind together the cathode active materials to preclude crack formation and prevent disintegration of the active materials on the surface of the current collector. The quantity of polymeric binder is in the range of 0.5% to 30% by weight.
Current manufacturing techniques for forming cathodes are both energy and time consuming. The synthesis of active material in present methods requires high temperature and harsh reaction conditions. Synthesis of the active material may also take several hours to several days to complete. Once synthesis of the active material is complete, the active material is combined with conductive additives, binders, and toxic and expensive solvents to make a slurry. The slurry is then deposited onto the positive current collector. The slurry coated on the current collector needs to go through a long and energy intensive drying process. Drying lines created to complete the drying of the slurry can be quite long depending on the output of the synthesis and deposition processes.
Accordingly, there is a need in the art for systems and methods which can quickly and more energy efficiently produce cathodes for energy storage devices.